Labour's threat to collapse power-sharing deals with the Green Party over their divisive 'Zionism is Racism' motion could plunge councils across the country into political turmoil.
Yesterday Labour said it is giving local Green Party branches seven days to disavow the motion passed at their Brighton conference earlier this month.
The new policy called for Israel to be treated like apartheid South Africa, and was branded a plan to destroy Israel itself.
After Andy Burnham ruled out national coalition talks with the Greens over their 'antisemitic' new position, Labour's chairman said the same will apply at local levels.
Bridget Phillipson said: 'Where local Labour Parties currently have an arrangement with the Greens in local government, we expect their Green counterparts to make clear that they reject this position and to call on their national leadership to reconsider the policy.
'We have asked local Green groups to respond as a matter of urgency. Where they are unable to provide that assurance, Labour will bring any such local arrangement to an end.
'This isn't an issue of party politics; it's about doing what is right and upholding the values anyone holding public office should share.'
Labour won plaudits for its tough stance, with Labour Against Antisemitism telling the Daily Mail they were 'relieved to see the Prime Minister listening to our concerns after we wrote to him'.
Zack Polanski's Greens could lose power in councils across England if Labour tears up coalitions and pacts with them over their new 'Zionism is Racism' motion
Green Party deputy leader Mothin Ali was a key advocate of the motion, passed at their conference earlier this week, issuing a warning to Mr Polanski to not overrule party members
But the new hardline position by Labour could threaten to spark chaos across councils in Britain, with more than a dozen currently involving Labour-Green pacts.
According to Mail analysis, if Labour withdraws from all councils where they have some form of agreement with the Greens, nine of the 14 could face a major threat to the existing ruling administration, with the current governing arrangements either breaking apart, or becoming substantially unworkable.
Eleven of the 14 councils would lose their current majorities, potentially opening the door to the Tories, Liberal Democrats or Reform.
Surprisingly many of the councils currently run by Labour-Green pacts are in some of the leafiest, most middle-class parts of the country.
Take a look below to see if your council could be set for political tumult next week, should its local Green Party branch refuse to disavow its party's new policy on Israel.
Sheffield
Current situation: Labour-led council propped up by the Greens. Labour-Green majority coalition, with 45/84 seats.
If Labour withdraws its agreement with the Greens, the governing majority disappears, with Labour far short of the 43 seats required.
Labour could attempt to continue as a minority administration, but it would need support from other parties
Lewes
Current situation: Labour props up Green-led council. Green/Labour majority coalition (26/41 seats)
Seats: Green (18), Liberal Democrat (14), Labour (8), Independent (1)
If Labour withdraws its agreement with the Greens, the coalition loses its majority and effectively ends in its present form.
Greens have 18 seats and Labour 8.
Without Labour, the Greens would be well short of the 21-seat majority threshold and would need a new arrangement.
Greens would probably seek a new agreement involving some combination of the 14 Lib Dems and/or the single independent.
Warwick
Current situation: Labour props up Green-led council. Green/Labour minority coalition (22/45 seats)
Seats: Green (15), Liberal Democrat (9), Independent (8), Labour (7), Conservative (5)
If Labour withdraws its agreement with the Greens, the existing Green/Labour administration effectively breaks apart.
The coalition is already one seat short of an outright majority. Removing Labour's seven councillors leaves the Greens with only 15 of 45 seats.
The Greens would need a replacement arrangement or would have to attempt to govern as a much smaller minority, potentially seeking support from the Lib Dems and/or independents.
Sheffield is one of the councils most at risk of political upheaval if Labour terminates its pact with the Greens
Lewes is also at risk, where Labour props up a green-led council with a tiny majority
In Oxford, Labour has a minority administration with an agreement for 'closer working' with the Greens on a number of issues
Forest of Dean
Current situation: Labour props up Green-led council through a confidence and supply arrangement. Green minority administration (15/38 seats)
Seats: Green (15), Independent (11), Conservative (6), Labour (4), Reform (1), Liberal Democrat (1)
If Labour withdraws its confidence and supply agreement, the Green administration loses its guaranteed Labour support on key votes.
The Greens would remain the largest governing group with 15 seats but would be far short of the 21 required for a majority.
The administration would not automatically fall, but its ability to survive key votes and pass its programme would become much less secure, requiring support or abstentions from other groups.
West Sussex
Current situation: Labour is part of a Liberal Democrat/Green/Labour/Independent majority 'rainbow' coalition (36/70 seats)
Seats: Liberal Democrat (23), Reform (23), Conservative (11), Green (7), Labour (5), Independent (1)
If Labour withdraws, the existing coalition loses its majority.
Removing Labour's five councillors leaves the Lib Dems, Greens and Independent with 31 of 70 seats, well short of the 36 required for a majority.
The Lib Dems and Reform are tied as the largest parties on 23 seats each, so Labour withdrawal could trigger substantial negotiations over who runs the council.
Broadland
Current situation: Labour is part of a Liberal Democrat/Labour/Green majority coalition (25/47 seats)
Seats: Conservative (19), Liberal Democrat (14), Labour (7), Green (4), Independent (2), Reform (1)
If Labour withdraws, the coalition loses its majority, and the existing administration cannot continue on the same numerical basis.
Without Labour's seven seats, the Lib Dems and Greens have 18 of 45 seats.
The Conservatives are the largest single party on 19 seats, so Labour withdrawal could lead to a new minority administration.
Havant
Current situation: Labour is part of a Labour/Green/Liberal Democrat coalition (18/36 seats)
Seats: Reform (10), Labour (7), Green (6), Liberal Democrat (5), Conservative (5), Independent (3)
If Labour withdraws, the existing three-party coalition is reduced to only 11 of 36 seats and cannot continue in its present form.
Labour itself has only seven seats, so it could not replace the coalition with a Labour administration on its own.
A new governing arrangement would have to be negotiated, with Reform the largest single party on ten seats and several different combinations potentially possible.
Arun
Current situation: Labour is part of a Liberal Democrat/Labour/Green/Independent majority coalition (33/54 seats)
Seats: Conservative (19), Liberal Democrat (14), Labour (8), Independent (6), Green (five), Reform (two)
If Labour withdraws, the existing coalition loses its majority.
Removing Labour's eight councillors leaves the Lib Dems, Greens and Independents with 25 of 54 seats, short of the 28 required for an outright majority.
The remaining partners could try to continue as a minority administration but would need outside support or abstentions to pass key business.
Derbyshire Dales
Current situation: Labour is part of a Liberal Democrat/Labour/Green majority coalition (22/35 seats)
Seats: Liberal Democrat (12), Conservative (nine), Labour (six), Green (four), Independent (four)
If Labour withdraws, the administration loses its majority.
Without Labour's six councillors, the Lib Dems and Greens have 16 of 34 seats, short of the 18 required for a majority.
They could potentially continue as a minority administration but would need support or abstentions from independents or other groups on key votes.
West Oxfordshire
Current situation: Labour is part of a Liberal Democrat/Labour/Green majority coalition (31/49 seats)
Seats: Liberal Democrat (19), Conservative (17), Labour (eight), Green (four), Reform (one)
If Labour withdraws, the remaining Lib Dem/Green administration loses its majority.
Without Labour's eight councillors, the Lib Dems and Greens have 23 of 49 seats, two short of the 25 required for an outright majority.
The Lib Dems and Greens could potentially continue as a minority administration but would need outside votes or abstentions to pass key business.
Coventry
Current situation: Labour minority administration propped up by the Greens through an informal arrangement, including two Green Scrutiny Board chairs (24/54 Labour seats)
Seats: Labour (24), Reform (20), Conservative (six), Green (four)
If Labour ends the arrangement with the Greens, Labour remains the largest party and could try to continue as a minority administration but loses dependable Green support.
Labour has 24 seats, four short of the 28 required for an outright majority.
Labour would therefore need support or abstentions from other groups to pass budgets and other contested business, and the Green scrutiny arrangements would likely need to be revisited.
North Somerset
Current situation: Labour is part of a Labour/Liberal Democrat/Green/Independent majority partnership administration (35/50 seats)
Seats: Conservative (12), Labour (ten), Liberal Democrat (nine), Green (eight), Independent (eight), Reform (three)
If Labour withdraws, the remaining Lib Dems, Greens and Independents would have 25 of 50 seats.
That is exactly half the council rather than an outright majority, so the remaining administration would lose its existing majority but would be much closer to retaining workable control than in most other affected councils.
The practical effect would depend on voting arrangements and whether the remaining partners could secure support or abstentions from elsewhere.
Oxford
Current situation: Labour minority administration (20/48 seats) with an agreement for 'closer working' with the Greens on a number of issues rather than a clearly described formal coalition or confidence and supply deal.
Seats: Labour (20), Green (13), Liberal Democrat (nine), Independent (six)
If Labour ends the closer-working arrangement, there may be less immediate structural change than in councils with a formal coalition.
Labour would remain a 20-seat minority administration and would continue to need support or abstentions from other groups to pass contested business.
Whether the national instruction requires this looser arrangement to end depends on whether Labour treats this case as a power-sharing arrangement.
West Devon
Current situation: Labour is part of the Independent/Green/Liberal Democrat/Labour 'West Devon Alliance' majority coalition (21/31 seats)
Seats: Independent (11), Conservative (ten), Green (six), Liberal Democrat (three), Labour (one)
If Labour withdraws, the effect on the administration is small.
Removing Labour's single councillor leaves the Independents, Greens and Lib Dems with 20 of 31 seats, still comfortably above the 16 required for a majority.
The existing alliance would need to change formally, but the remaining partners could continue to control the council without Labour.